This invention relates to an apparatus for preparing the edges of metal sheets to be welded, comprising an assembly of metal working means, in particular milling cutters, included in a unit which is associated with means for producing between the sheet and the unit a relative movement during which said metal working means are working an edge of the sheet.
Swedish patent specification No. 170,283 describes an edge preparation apparatus of the above-indicated general type comprising a metal working unit which is movable along the upper edge of a substantially vertically positioned sheet and which, as metal working means, includes an assembly of milling cutters suited both for face milling and for bevelling said edge. This working unit is in the form of a carriage divided into two parts, viz. a first part which is provided with wheels and is movable along a rectilinear guide by means of a chain drive, and a second part which supports the milling cutters and is vertically displaceable with respect to the first part to adjust the apparatus to sheets of different width. The sheet subjected to machining is carried at its lower edge by a roller bed including a plurality of lying supporting rollers and a plurality of standing guide wheels against which one side of the sheet bears. In the area of its upper edge, the sheet, in its upright position, is maintained by a pair of supporting wheels which are mounted on and accompany the movable carriage. The purpose of this construction is to permit the sheet, under the influence of any curved portions or sinuosities that may exist in the sheet, to pivot its lower edge, with the supporting wheels constituting a centre of oscillation, according as the curved portions during the travel of the carriage along the edge of the sheet being machined, enter into engagement with the milling cutters.
The above-described apparatus may possibly be capable of working relatively thin and light sheets in an acceptable way. However, for thick and heavy sheets (e.g. up to 22.times.4.5 m and with a thickness of 30-40 mm), it is useless in actual practice. For sheets weighing some tens of tons, the sheet is simply unable to oscillate with its lower edge in the intended way, which means that the sheet will have a bending effect on the milling and carriage equipment. Another shortcoming of the known apparatus is that the sheets must necessarily be held in an upright position. This means that the sheets, in a complicated and time-consuming way, must be turned after a first edge has been finally machined and before the opposite edge should be worked. Further, this prior art apparatus suffers from a poor machining capacity since only one edge can be worked in each machining operation in that the lower edge of the sheet must always be resting on the roller bed and, hence, is not accessible for milling.
Swedish published application No. 368,916 describes an apparatus for simultaneously milling the surfaces of two edges, facing each other, of two adjacent sheets. In this known apparatus, the sheets are clamped fast by means of electromagnets, and a carriage which at its upper end carries a milling body is advanced along a rail located on a level below the sheets. This apparatus has no drive rollers at all that can follow the edge portions of the sheets and possible sinuosities thereon. Thus, this apparatus is suited exclusively for milling the faces of the sheet edges, but not for bevelling them.
Nor has the apparatus disclosed in Swedish published application No. 7514613-4 any drive rollers that can follow the edge of the sheet. On the contrary, the metal working unit employed is advanced along a guiding device disposed beside the sheet.
Federal Republic of Germany patent specification No. 715780 discloses an apparatus for bevelling pipe ends. However, this apparatus has only one set of rollers and, therefore, is not capable of maintaining the apparatus with respect to a straight, lying sheet once the metal working means have passed the end of the sheet. Further, the oblique grooves provided on the drive rollers of the known apparatus do not in actual practice efficiently approach the metal working means and the pipe end to each other.